1. Field of the Invention
The present invention relates to an organic electroluminescence (hereinafter abbreviated simply as “EL”) panel having organic EL elements provided in a matrix form and a plurality of thin film transistors for driving the organic EL elements, both of which are formed on a substrate.
2. Description of the Related Art
Organic EL display panels are known as a type of flat display panel. Unlike liquid crystal display (LCD) panels, the organic EL display panels are self-emissive and commercialization of organic EL display panels in flat display panels which are bright and clear is highly expected.
An organic EL display is constructed by placing a plurality of pixels each having an organic EL element in an matrix form. As a method for driving the organic EL element, similar as in LCDs, a passive method and an active method are known. Of these, also similar to LCDs, the active matrix method is generally considered more desirable. That is, an active matrix method in which one or more switching elements (typically, one for switching and one for driving) are provided for each pixel and the display in each pixel is controlled by controlling the switching element is more advantageous than a passive method which does not have a switching element for each pixel, because the active matrix method enables higher resolution display.
An organic EL element emits light when an electric current is applied through an organic emissive layer. In order to enhance the emission capability, in many cases, a hole transport layer composed of an organic compound and/or an electron transport layer composed of an organic compound are provided adjacent to the organic emissive layer. These organic layer are easily degraded by moisture.
To address this problem, in an organic EL display, the region above the organic EL element is commonly covered by a metal cathode, a space above a display region (a region where a pixel is formed) in which an organic EL element is placed is sealed to form an airtight space, and a desiccant is placed within the airtight space to remove excess moisture.
However, conventional organic EL display panels configured in this manner have, in many cases, insufficient lifetime. After extensive study of the panels, the present inventors have found that in many cases the lifetime is unnecessarily shortened because the desiccant in the space above the organic EL element is insufficient. That is, in many cases, intrusion of moisture from the outside is not prevented to a sufficient degree.